It is well known that museum pieces, such as works of art, ancient manuscripts, archeological objects, etc., can be sensitive to the surrounding environmental conditions of humidity, temperature, and even microorganisms in the air. Thus, exposing the display piece to the surrounding environment can result in the object's degradation over an extended period of time. It is for this reason that many articles are displayed in a glass or plastic case which has some mechanism to control the environment within the case.
The interior environmental condition of a small enclosure is called a microclimate. Such an enclosure with a controllable microclimate is ideal for displaying or storing sensitive objects. One common type of display enclosure known in the art has a removable transparent cover, a stand which supports the object on display, and a seal under the cover for limiting outside air flow to and from the microclimate. The display case microclimate is typically controlled by a humidity buffer, usually silica gel, carried in an open vessel within the enclosure. Silica is an inert material having a pre-conditioned value for the absorption and desorption of moisture. The silica gel maintains a constant relative humidity level within the microclimate.
However, leakage of outside air into the microclimate through the seal or cover, which often occurs after a period of time, causes the silica gel to reach equilibrium with the outside air and disrupts the controlled microclimate. If the seal is inadequate, leaks can disrupt the microclimate quite rapidly. Restoration of the microclimate to the desired condition generally requires the removal of the seal and the replacement of the humidity buffer. Access to the humidity buffer often requires removal of the seal in order to remove the display cover, thereby exposing the object on display to the outside air. Once a seal is removed, it generally does not provide proper airtight sealing upon re-use. Hence, the seal must often be replaced. Therefore, maintenance of the typical sealed museum display case is a significant problem, particularly when servicing is required every few months.
Another prior art display case maintains a sealed microclimate by attaching a metal frame around the lower edge of the display cover. The frame has one or more grooves for holding a seal. The frame is screwed to a base, resulting in a seal between the base and the cover. However, subsequent removal of the cover to maintain the humidity buffer to restore the desired microclimate conditions requires the removal of a number of screws. This removal procedure results in the exposure of the display object to the outside air for at least a few minutes, thereby disturbing the controlled microclimate. Additional problems in this type of case are often caused by human error in fastening the frame to the base. Each screw causes a deformation or stress point on the O-ring seal, because each screw cannot be fastened with exactly uniform torque. Consequently, this prior art sealing mechanism often allows constant leakage of the outside air to the microclimate.
Still another type of prior art display case provides a separate lower chamber for the humidity buffer, located under the support platform for the object on display. In some designs, this lower chamber consists of shelves or a pan built into the supporting pedestal or stand, with a large access port for servicing the humidity buffer. In another design, the lower chamber has an internal sloping shelf, a first access port adjacent to the upper edge of the shelf, a second access port adjacent to the lower edge of the shelf, and a number of humidity buffer cylinders resting on the shelf. To replace a humidity buffer, the two ports are opened and the humidity buffer adjacent to the lower shelf edge is removed through the access port. The humidity buffer cylinders then roll down the shelf, providing a space at the top edge of the shelf wherein a new cylinder can be placed.
Although the aforementioned display case is somewhat effective in maintaining the internal microclimate, it still allows a significant amount of outside air flow to enter the display case through the access ports each time the case is serviced. Additionally, cylindrically-shaped humidity buffers must be used in order to roll down the slanted shelves. Furthermore, this elaborate humidity buffer replacement technique must be designed and constructed into the display case, i.e., it cannot be retrofit into an existing display case. Moreover, this type of display case cannot be removed as a sealed unit from its pedestal base.
This type of prior art display case also has inter-engaging adjustable latches, which maintain a frame and seal against the base. The frame includes a U-shaped groove, which mates with a deformable gasket affixed to the lower edge of the top cover. Latches of this type can often result in uneven tension on the seal. Moreover, the adjustment to the latches allows for unpredictable clamping pressure to be exerted on the seal.
Thus, problems presently exist with the seals and with access to the humidity buffer. Inadequate seals result in the need for frequent service or replacement of the humidity buffer. Previous means of access to the humidity buffer result in exposure of the art object to the outside air. Further, access to the object results in exposure of the humidity buffer to the outside air. Therefore, a need exists for an improved display case which minimizes the need for constant servicing of the humidity buffer, and which simplifies the maintenance and storage procedures.